Original hybrid control for robotic structures using magnetic shape memory alloys actuators.

International audienceMagnetic Shape Memory Alloys (MSMA) are relatively new active materials but at this time they are not actually very used as actuators despite a high strain and a small response time. This is probably due in part to a large hysteresis and a strong non-linear behaviour. In this paper, an original hybrid control is designed taking into account dynamical effects and hysteretic behaviour in order to increase static gain of the system. After a short presentation of MSMA behaviour, a modelling is proposed to obtain two different control strategies. Some experimental results are also given

Conversion d'Energie Magnéto-Thermo-Mécanique dans les Alliages à Mémoire de Forme Magnétiques.

National audienceLes alliages à mémoire de forme magnétiques sont des matériaux actifs dont les caractéristiques combinent celles des alliages à mémoire de forme classiques et celles des matériaux magnétostrictifs. Ces matériaux relativement récents sont actuellement assez peu utilisés pour des applications pratiques telles que les actionneurs et les capteurs en raison des difficultés de conception et de contrôle résultant d'un comportement complexe. Cet article se propose de présenter le mode de conversion d'énergie à l'oeuvre dans ces matériaux ainsi qu'un état de l'art des principaux travaux en termes d'actionneurs. Il se propose ensuite de présenter les réalisations des auteurs ainsi que les modèles de comportement développés pour finir par une présentation des règles de conception et de contrôle mis en évidence

Magnetic shape memory alloy and actuator design.

International audienceIn the field of micromechatronics, microrobotics and specially microfactories, active materials are used in most cases. They permit high resolution and distributed actuation. In this area, Magnetic Shape Memory Alloys (MSMA) are possible candidates. If a lot of studies deal with MSMA, only few applications use them until now. MSMA are attractive active materials because they have large strain (about 10%) as the classical shape memory alloys (SMA), but can provide a 100 times shorter time response. The main disadvantages of MSMA based actuators are the brittleness of the single-crystal material, the difficulty to apply the strong magnetic field required to obtain sufficient strain and the nonlinear behaviour. We propose in this paper a novel MSMA based actuator changing the disadvantage of the hysteretic behaviour into an advantage. This device is a push-pull actuator: two pieces of MSMA material act in an opposite way. The magnetic fields are created by coils and concentrated by ferromagnetic circuits. In order to move the central part of the actuator, a current pulse in the first coil is generated. The hysteretic behaviour of the material permits to keep a stable position when no current is applied. A current pulse in the second coil permits to displace the central part in the opposite direction. The stable position depends on the magnitude and the time duration of the current pulses and an infinity of stable positions can be reached. The use of current pulses permits also a reduction of the coil heating (Joule effect losses) and a reduction of the magnetic circuit size. The performances and characteristics of MSMA are between these of classical SMA and these of piezo-electric materials. A thermo-magneto-mechanical model of our actuator is currently in development in order to design an efficient control law welladapted to the specific MSMA properties

Multistable actuator based on magnetic shape memory alloy..

International audienceMagnetic Shape Memory Alloys (MSMs) are attractive smart materials because they exhibit, at the same time, a large strain (10 %) and a short time response (100 microns s). In this paper, we propose a novel MSM based actuator exploiting the characteristics of MSMs. This device is a push-pull actuator where two pieces of MSM act in an opposite way. The magnetic fields are created by two magnetic coils supplied by current pulses. The hysteretic behaviour of the MSM permits to keep a stable position when no current is applied and so limits heat losses in the coils. A model of this actuator is proposed and validated by experiments. A precise position feedback control of the actuator is then achieved using a displacement laser sensor

Nonlinear Hamiltonian modelling of magnetic shape memory alloy based actuators.

International audienceThis paper proposes an application of the Lagrangian formalism and its Hamiltonian extension to design, model and control a mechatronic system using Magnetic Shape Memory Alloys. In this aim, an original dynamical modelling of a Magnetic Shape Memory Alloy based actuator is presented. Energy-based techniques are used to obtain a coherent modelling of the magnetical, mechanical and thermodynamic phenomena. The Lagrangian formalism, well suited in such a case, is introduced and used to take into account the dynamical effects. Hamilton equations are deduced and used for the computation of the theoretical behaviour of this actuator. These numerical simulations are compared with some experimental measurements permitting the validation of the proposed modelling. Beyond the work presented here, these results will be used to design an energy shaping nonlinear control well-adapted for a strongly nonlinear active material

Modelling Rearrangement Process of Martensite Platelets in a Magnetic Shape Memory Alloy Ni2MnGa Single Crystal under Magnetic Field and (or) Stress Action

International audienceThe aim of the paper is the modelling of the rearrangement process between martensite variants in order to use Magnetic alloys (MSMs) as actuators. In the framework of the thermodynamic of irreversible processes, an efficient choice of the internal variables in order to take into account the magnetic and the mechanical actions and a free energy function are stated. The behaviour is chosen as magnetically reversible and mechanically irreversible. An equivalence between magnetic field action H and uniaxial stress action o for the initiation of the rearrangement is established. Finally, moel predictions are compared with experimental measurements

Modeling and control of micro-mechatronic devices : application of variational and energetic methods for micro-actuator design.

International audienceThis paper is focused on a modeling procedure wellsuited for the design of micro-mechatronic systems and especially for micro-actuators. The purpose of this publication is to show that the variational and energetical methods is not only wellsuited to model classical micro-mechatronic devices but that they are also well-suited to include complex dynamical behaviour such as non-linearity and hysteretical behaviour. This procedure is applied to the design of a new actuator using one of the relatively new smart materials, the Magnetic Shape Memory Alloys (MSMAs). It should be stressed that the presented approach can be extented to a great range of other smart materials and that the description can be easily extented up to the control level

Conversion d'énergie magnéto-thermo-mécanique dans les alliages à mémoire de forme magnétiques.

National audienceLes matériaux actifs sont de plus en plus utilisés en tant qu'actionneurs dans les systèmes mécatroniques et micro-mécatroniques. Les matériaux piézoélectriques et les alliages à mémoire de forme sont les deux exemples les plus représentatifs à l'heure actuelle dans ces domaines. Les alliages à mémoire de forme magnétiques sont des matériaux relativement récents et ils apparaissent très intéressants de par leur rapidité d'actionnement et leur grande déformation ; cependant, leur comportement fortement non-linéaire reste un frein à leur développement et les méthodes de conception et de commande les concernant se doivent d'évoluer

Modélisation hamiltonienne de systèmes non linéaires micro-mécatroniques. Application au développement et au contrôle d'actionneurs en AMFM.

National audienceCet article propose d'appliquer le formalisme de Lagrange et plus particulièrement son extension hamiltonienne pour concevoir, modéliser et contrôler des systèmes micro-mécatroniques. Dans ce but, la modélisation dynamique originale d'un actionneur à base d'Alliage à Mémoire de Forme Magnétique (AMFM) sera présentée. Cette modélisation de type énergétique est mise en oeuvre dans le but d'obtenir une formulation homogène entre magnétisme, dynamique du solide et thermodynamique des processus irréversibles utilisée pour l'étude des matériaux actifs. Le formalisme hamiltonien bien adapté à cette tâche est alors introduit et utilisé. Cet article propose quelques rappels sur ce formalisme ainsi que sur les AMFM. Il pose ensuite l'écriture d'un hamiltonien divisé en trois parties étudiées séparément puis les équations de Hamilton qui sont alors utilisées afin d'obtenir le jeu d'équations complet utilisé dans des simulations, ce qui permettra, au delà du travail présenté ici, d'utiliser le modèle dansle cadre d'une commande non-linéaire de type modelage d'énergie (energy shaping)